1. Field of the Invention
The present invention relates to an ultrasonic imaging apparatus for generating ultrasonic images based on reception signals obtained by transmitting ultrasonic waves and receiving ultrasonic echoes, and an ultrasonic image processing apparatus for processing image data in such an ultrasonic imaging apparatus. Further, the present invention relates to an ultrasonic image processing method and an ultrasonic image processing program to be used in such an ultrasonic image processing apparatus.
2. Description of a Related Art
In medical fields, various imaging technologies have been developed in order to observe the interior of an object to be inspected and make diagnoses. Especially, ultrasonic imaging for obtaining interior information of the object by transmitting and receiving ultrasonic waves enables image observation in real time and provides no exposure to radiation unlike other medical image technologies such as X-ray photography or RI (radio isotope) scintillation camera. Accordingly, ultrasonic imaging is utilized as an imaging technology at a high level of safety in a wide band of departments including not only the fetal diagnosis in the obstetrics, but also gynecology, circulatory system, digestive system, etc.
The ultrasonic imaging is an image generation technology utilizing the nature of ultrasonic waves that they are reflected at a boundary between regions with different acoustic impedances (e.g., a boundary between structures). Therefore, the outline of a structure (e.g., internal organs, diseased tissues, or the like) existing within an object to be inspected such as a human body can be extracted by transmitting an ultrasonic beam into the object, receiving ultrasonic echoes generated within the object, and obtaining reflection points, where the ultrasonic echoes are generated, and the reflection intensity.
By the way, in an ultrasonic image in which an object having a nonuniform structure like a living body is imaged, a pattern, in which bright parts and/or dark parts are scattered, appears. Such a pattern is called a speckle pattern, and generated, for example, by interference between ultrasonic echoes reflected by nonuniform tissues existing within an internal organ or the like. This speckle pattern is a kind of virtual image, and thereby, the detected outline of the structure or the like often becomes unclear.
Japanese Patent Application Publication JP-P2003-61964A discloses an ultrasonic diagnostic apparatus for smoothing images by utilizing statistical characteristics of a speckle pattern and extracting minute structures to observe minute abnormal lesions within a homogeneous tissue structure such as the stage of liver cirrhosis progression. This ultrasonic diagnostic apparatus includes analysis calculation means for extracting a particular signal by using intensity of echo signals generated from a part of an object to be inspected or the statistical characteristics of amplitude information, and display means for displaying a result extracted by the analysis calculation means (page 1, FIG. 1).
Further, Japanese Patent Application Publication JP-P2004-41617A discloses an ultrasonic diagnostic apparatus usable for tissue diagnoses by quantifying the fineness of a speckle pattern contained in an ultrasonic image. This ultrasonic diagnostic apparatus includes image forming means for forming an ultrasonic image based on echo data obtained by transmitting and receiving ultrasonic waves, binarization processing means for generating plural binarized images by performing binarization processing on the ultrasonic image while varying threshold levels, region factor means for obtaining the number of independent regions having high brightness or low brightness by performing labeling processing with respect to each of the binarized images, and graph creating means for creating a speckle evaluation graph representing the number of individual regions at each of the threshold level (page 1). According to this ultrasonic diagnostic apparatus, since the created speckle evaluation graph reflects tissue properties, tissue diagnoses can be made by performing numerical analysis on the graph. Further, JP-P2004-41617A also discloses that processing of emphasizing speckles (processing of removing base components) is performed prior to binarization processing, and that an image before binarization and an image after binarization are simultaneously displayed.
Further, in Kamiyama et al., “Tissue Characterization Using Statistical Information from Ultrasound Echo Signals”, MEDICAL IMAGING TECHNOLOGY, Vol. 21, No. 2, March 2003, pp. 112-116, the general characteristics and statistical characteristics of a speckle pattern appearing in an ultrasonic tomographic image is described and study on tissue property diagnoses utilizing such statistical characteristics of the ultrasonic signal is introduced.
As described above, in ultrasonic diagnoses, speckles appearing in ultrasonic images are extracted, analyzed and displayed according to diagnostic purposes. Since it is considered that spackles contain information relating to tissue properties, it can be usable for diagnoses of tissue properties to extract and display the speckles. However, the ultrasonic diagnostic apparatuses disclosed in JP-P2003-61964A and JP-P2004-41617A are for analysis within a preset region of interest and for displaying still images of speckles. In order to further effectively utilize the information relating to the tissue properties contained in the speckles, it is desirable that speckle information contained in the entire ultrasonic image can be analyzed and the analysis results can be displayed as a moving image. Also, it is considered that users desire such a function.
Here, as described in Kamiyama, et al., it is conceivable that the spatial frequency components of a speckle pattern become relatively high in an ultrasonic image because the speckle pattern is produced by interference between ultrasonic waves. Accordingly, if an ultrasonic image in a specific relatively high frequency band can be displayed as a moving image, it would lead to extracting the speckle pattern easier and supporting diagnosis of tissue properties. However, in the present circumstances, no ultrasonic imaging apparatus having such a function has been proposed.